1. Field of the Invention
The present invention relates to image pickup apparatuses.
2. Description of the Related Art
In related art, an image pickup apparatus, such as a video camcorder, is provided, which includes an image-pickup optical system, a color separation prism constituted by three prisms that separate incident light guided by the image-pickup optical system into three light components of the three primary colors and emit the three light components, and three image pickup elements that respectively receive the three light components emitted from the three prisms of the color separation prism so as to produce image signals. See Japanese Unexamined Patent Application Publication No. 2006-186936 for an example of such an image pickup apparatus.
With regard to a light beam transmitted through the image-pickup optical system, there is a portion of the light beam which travels through the vicinity of an edge of each of the prisms, when the color separation prism is viewed from the optical-axis direction of the image-pickup optical system.
When this portion of the light beam enters the edges of prisms, the light beam is reflected, refracted, and scattered at these edges, thus producing extraordinary light. If this extraordinary light reaches the image pickup elements, a problem may occur, such as flare formed on picked-up images.
To prevent such flare, a fixed aperture stop is provided between the color separation prism and a final lens, which is disposed closest to the color separation prism, of a plurality of lenses constituting the image-pickup optical system.
Specifically, the fixed aperture stop has an aperture that limits the incident light. An edge section of the aperture blocks the portion of the light beam traveling through the vicinity of the edges so as to prevent the portion of the light beam from reaching the edges. Normally, an effective image pickup range in an image pickup face of each image pickup element is horizontally oblong such that the horizontal axis of the effective image pickup range is greater than the vertical axis thereof.
Therefore, by arranging the image pickup elements along the shorter-side direction thereof (i.e., the vertical direction thereof), the space occupied by the image pickup elements and the prisms can be reduced, which is advantageous toward achieving size reduction. In this case, the directions of color separation by the color separation prism are orthogonal to the faces of the prisms that face the corresponding image pickup elements (i.e., the faces from which the color-separated light components are released), and the edges of the prisms are located above and below the optical path of the image-pickup optical system.
A light beam that causes problems like flare is a light beam that passes through the vicinity of the edges of the color separation prism. This implies that a light beam that should be limited by the fixed aperture stop is a light beam that travels above and below the optical path of the image-pickup optical system. Therefore, the light-beam limitation by the fixed aperture stop should be carried out actively above and below the optical path of the image-pickup optical system.
On the other hand, the longer-side direction (i.e., the horizontal direction) of the image pickup elements is orthogonal to the directions of color separation and is not directly relevant to the color separation. Therefore, it may not be necessary to actively carry out the light-beam limitation by the fixed aperture stop with respect to the horizontal direction.
Thus, the edge section in the fixed aperture stop has linear segments and arc segments. Specifically, as viewed from the optical-axis direction of the final lens, the linear segments each extend on an imaginary line orthogonal to an imaginary line extending along the optical axis, and the linear segments are provided at two opposite locations of the edge section and extend parallel to each other.
The two linear segments are used for limiting a light beam traveling above and below the optical path of the image-pickup optical system.